如何检查字母在PHP中是大写还是小写? [英] How to check if letter is upper or lower in PHP?

问题描述

我在UTF-8中也有带变音符号的文本，并且想检查该文本的首字母是大写还是小写.该怎么做?

I have texts in UTF-8 with diacritic characters also, and would like to check if first letter of this text is upper case or lower case. How to do this?

推荐答案

与在此发布的其他解决方案相比，我认为进行preg_呼叫是最直接，简洁和可靠的呼叫.

It is my opinion that making a preg_ call is the most direct, concise, and reliable call versus the other posted solutions here.

echo preg_match('~^\p{Lu}~u', $string) ? 'upper' : 'lower';

我的模式细分:

~      # starting pattern delimiter 
^      #match from the start of the input string
\p{Lu} #match exactly one uppercase letter (unicode safe)
~      #ending pattern delimiter 
u      #enable unicode matching

当这组测试导致ctype_和< 'a'失败时，请注意.

Please take notice when ctype_ and < 'a' fail with this battery of tests.

代码:(演示)

$tests = ['âa', 'Bbbbb', 'Éé', 'iou', 'Δδ'];

foreach ($tests as $test) {
    echo "\n{$test}:";
    echo "\n\tPREG:  " , preg_match('~^\p{Lu}~u', $test)      ? 'upper' : 'lower';
    echo "\n\tCTYPE: " , ctype_upper(mb_substr($test, 0, 1))  ? 'upper' : 'lower';
    echo "\n\t< a:   " , mb_substr($test, 0, 1) < 'a'         ? 'upper' : 'lower';

    $chr = mb_substr ($test, 0, 1, "UTF-8");
    echo "\n\tMB:    " , mb_strtoupper($chr, "UTF-8") == $chr ? 'upper' : 'lower';
}

输出:

âa:
    PREG:  lower
    CTYPE: lower
    < a:   lower
    MB:    lower
Bbbbb:
    PREG:  upper
    CTYPE: upper
    < a:   upper
    MB:    upper
Éé:               <-- trouble
    PREG:  upper
    CTYPE: lower  <-- uh oh
    < a:   lower  <-- uh oh
    MB:    upper
iou:
    PREG:  lower
    CTYPE: lower
    < a:   lower
    MB:    lower
Δδ:               <-- extended beyond question scope
    PREG:  upper  <-- still holding up
    CTYPE: lower
    < a:   lower
    MB:    upper  <-- still holding up

如果有人需要区分大写字母，小写字母和非字母，请参见这篇文章.

If anyone needs to differentiate between uppercase letters, lowercase letters, and non-letters see this post.

它可能将这个问题的范围扩大了很多，但是如果您的输入字符特别是松散的(它们可能不存在于Lu可以处理的类别中)，则您可能需要检查第一个字符是否有大小写变体:

It may be extending the scope of this question too far, but if your input characters are especially squirrelly (they might not exist in a category that Lu can handle), you may want to check if the first character has case variants:

\ p {L&}或\ p {Cased_Letter}:存在小写和大写变体(Ll，Lu和Lt的组合)的字母.

\p{L&} or \p{Cased_Letter}: a letter that exists in lowercase and uppercase variants (combination of Ll, Lu and Lt).

• 来源: https://www.regular-expressions.info/unicode.html
• Source: https://www.regular-expressions.info/unicode.html

要包含带有SMALL变体的罗马数字(数字字母")，可以在必要时将额外的范围添加到图案中.

To include Roman Numerals ("Number Letters") with SMALL variants, you can add that extra range to the pattern if necessary.

https://www.fileformat.info/info/unicode /category/Nl/list.htm

代码:(演示)

echo preg_match('~^[\p{Lu}\x{2160}-\x{216F}]~u', $test) ? 'upper' : 'not upper';

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